The disclosure relates to a gear machine having the features of the disclosure.
DE 10 2009 012 853 A1 discloses a gear machine which can be operated as a pump or as a motor. The gear machine comprises two externally intermeshing gear wheels, which are enclosed by a housing. The housing comprises a high-pressure connection and a low-pressure connection situated opposite one another.
When the gear machine is operated as a pump, one of the gear wheels is set in rotational motion, for example by an electric motor, pressure fluid, in particular hydraulic oil, flowing from the low-pressure connection to the high-pressure connection. When the gear machine is operated as a motor, the pressure fluid flows from the high-pressure connection to the low-pressure connection, thereby setting the gear wheels in rotational motion.
In the direction of a central axis the low-pressure connection has a constant cross sectional shape, which is of circular design. The aim is to make the corresponding circle diameter as large as possible at the low-pressure connection, in order that low rates of flow of the pressure fluid occur at this connection. This serves to prevent cavitation on the low-pressure connection, particularly in the case of pumps with rapidly rotating gear wheels.
Here the scope for increasing the diameter of the low-pressure connection is limited by the need to maintain an adequate seal between the high-pressure connection and the low-pressure connection at the gear tooth tips of the gear wheels.
Attention must be drawn in this context to the pressure equalization chamfer on the bearing liners. The bearing liners are arranged on both sides next to the gear wheels and are pressed tightly against the lateral faces of the gear wheels by the pressure fluid. Here the gear wheels are supported by circular cylindrical bearing journals in the bearing liners. The bearing liner on one side of the gear wheels may be formed in one piece, but it is equally feasible to assign a separate part of the bearing liner to each gear wheel.
At least one pressure equalization chamfer on the bearing liners, which is arranged opposite the lateral faces of the gear wheels and the inner circumferential face, is assigned to each gear wheel. Here the inner circumferential face is the face against which the gear tooth tips of the gear wheels tightly bear. The pressure equalization chamfer extends from the high-pressure connection in the direction of the low-pressure connection. The pressure at the high-pressure connection therefore prevails in all tooth spaces of the gear wheels which are situated opposite the pressure equalization chamfer, so that in the area of the low-pressure connection the gear wheels are pressed tightly against the inner circumferential face of the housing with an accurately predictable force, in order to bring about sealing there.
In dimensioning the diameter of the low-pressure connection, it must be ensured that in no rotational position of the gear wheels does a fluid exchange connection exist between the pressure equalization chamfer and the low-pressure connection by way of the tooth spaces.
The object of the disclosure is to prevent cavitation at the low-pressure connection in rapidly rotating gear machines, especially pumps, or to allow this to occur only at higher rotational speeds of the gear wheels.